Air compressors for use on railway cars are well known. For example, the prior art includes an apparatus described in Japanese Utility Model Application No. 60-17472, previously filed by the present applicants, and illustrated in FIGS. 3 and 4. As illustrated therein, the electromotive air compressor unit consists of the motor 3 and the air compressor 6. Both of these units are hung under the floor 2 of the railroad car by means of the hanger 5 in a manner such that they become parallel to the above-mentioned floor 2 and same shaft and, at the same time, they are coupled by means of the coupling 12 so that the torque of the motor 3 can be transferred to the air compressor 6. In addition, the air sucked in via the intake air filter and the intake muffler 27 is conducted into two low pressure cylinders 13 and is compressed, after which it is cooled by the intercooler 18 and it is distributed into two high-pressure cylinders 14 and compressed. Thereafter, the air is combined and conducted to the cooler located downstream, which is not shown in the FIGURES.
Generally, the underside of the floor of a railroad car of a modern transportation system, etc., is provided with numerous instruments and equipment, etc., so that space tends to be generally limited. Therefore, the miniaturization of the equipment and instrumentation installed under the floor or some other improvements to the installations have been desired.
However, when the motor and the air compressor are hung parallel to the floor, as can be seen in the above-mentioned example of the prior art of the electromotive air compressor, space is required for both the motor and the air compressor, which reduces the space available for the installation of the other equipment by that amount. In addition, in the radial reciprocating air compressor described in Japanese Patent No. 59-5797 and Japanese Patent Application No. 60-281563, the cylinder becomes head-low, so that the lubricant flows into the cylinder and it becomes unusable, all of which represent significant disadvantages.